R: Assert a length

L {pkgutils}

R Documentation

Assert a length

Description

Raise an error if one to several given R objects do not have the specified length. This is mainly used to easily generate meaningful error messages related to function arguments.

Usage

  L(x, .wanted = 1L,
    .msg = "need object '%s' of length %i",
    .domain = NULL)

  LL(..., .wanted = 1L,
    .msg = "need object '%s' of length %i",
    .domain = NULL)

Arguments

`x`	R object to test.
`...`	Any R objects to test.
`.wanted`	Integer scalar giving the desired length. Note that this can not be a scalar with ‘double’ as `storage.mode`.
`.msg`	Error message passed to `sprintf` with the name of `x` and the value of `wanted` as the two additional arguments.
`.domain`	Passed to `stop` from the base package as argument ‘domain’.

Value

If successful, L returns x, but an error message is raised if length(x) is not identical to wanted. LL yields the names of the arguments contained in ..., returned invisibly, if successful. Otherwise an error is raised.

Examples

(x <- L(letters, 26L))

##  [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q"
## [18] "r" "s" "t" "u" "v" "w" "x" "y" "z"

stopifnot(identical(x, letters))
(x <- try(L(letters, 25L), silent = TRUE))

## [1] "Error : need object 'letters' of length 25\n"
## attr(,"class")
## [1] "try-error"
## attr(,"condition")
## <simpleError: need object 'letters' of length 25>

stopifnot(inherits(x, "try-error"))
(x <- LL(letters, LETTERS, .wanted = 26L))

## [1] "letters" "LETTERS"

stopifnot(x == c("letters", "LETTERS"))